Color characteristic measuring apparatus and method, and storage medium of image pickup data

ABSTRACT

It is an object of the invention to measure the precise color characteristic of an image pickup machine and accurately reproduce a subject in an image display unit. 
     A color characteristic measurement apparatus which has a test chart ( 1 ) as a subject of an image pickup machine ( 6 ), a hole ( 2 ) made in the test chart ( 1 ), a black box ( 3 ) placed on a rear face of the test chart ( 1 ) and formed on an inner surface in black, and a light output section ( 4 ) placed in the black box ( 3 ) at a position where the light output section ( 4 ) can be observed through the hole ( 2 ) from the outside.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP97/04669 which has an Internationalfiling date of Dec. 18, 1997, which designated the United States ofAmerica.

TECHNICAL FIELD

This invention relates to a color characteristic measurement apparatus,a color characteristic measurement method, and an image pickup datastorage medium and in particular to an apparatus and a method formeasuring the color characteristic of an image pickup machine such as adigital video camera or a digital still camera or measuring andcorrecting the color characteristic and a storage medium for storingimage data picked up by an image pickup machine.

BACKGROUND OF THE INVENTION

A typical color characteristic measurement apparatus and method of animage pickup machine in a related art are shown in Section 3, Clause 18of “International Standard IEC 1146-1 Video cameras(PAL/SECAM/NTSC)—Method of Measurement—Part 1: Non-broadcasting singlesensor cameras” published in May 1994 by IEC (InternationalElectrotechnical Commission) as international standard.

FIG. 48 is a drawing to show the configuration of an apparatus formeasuring color and gradation characteristics of a digital still camerawhich is used as an example of an image pickup machine, as applicationof such a measurement apparatus and method in the related art. In thefigure, numeral 6 denotes an image pickup machine such as a digitalstill camera whose color characteristic is to be measured, numeral 1denotes a test chart of a subject of the image pickup machine 6, numeral5 denotes an illumination light source having stable illuminationintensity and color temperature for illuminating the test chart 1, andnumeral 19 denotes a computer for receiving data output from the imagepickup machine 6.

FIG. 49 is a format drawing of the test chart 1 containing white, black,a gray scale 200 changing gradually from white to black, and severalcolor charts 210 of red, green, blue, etc., as reference colors. Asexamples of these color charts, the characteristics are defined in AnnexA and Annex B of the above-mentioned international standard.

First, the R, G, and B values of the color charts 210 of the test chart1 shown in FIG. 49 are assumed to be already known and are adopted astheoretical values. For example, if data consists of eight bits, ideallyR=255 and G=B=0 for red, G=255 and R=B=0 for green, and B=255 and R=B=0for blue.

Next, the differences between the R, G, and B values corresponding tothe color charts 210 measured when an image of the test chart 1 ispicked up by the image pickup machine 6 and the theoretical R, G, and Bvalues (color differences) are found, whereby the color reproducibilityof the image pickup machine 6 can be evaluated.

The gradation characteristic of the image pickup machine 6 can be foundfrom the measurement values provided when the gray scale 200 changinggradually from white to black is imaged by the image pickup machine 6.

However, the illumination intensity and chromaticity on the face of thetest chart illuminated by the illumination light source vary from oneposition to another. Thus, if a photograph of the same color chart istaken, the measurement value varies depending on the position on thetest chart and unless illumination intensity and chromaticityinconsistencies are corrected, precise values cannot be provided.

If a photograph of the same color chart is taken even under idealuniform illumination, the measurement value varies depending on thecharacteristics of the image pickup optical system of the image pickupmachine, for example, because of the light quantity difference betweenthe center and peripheral portions. Thus, unless the characteristics ofthe image pickup optical system of the image pickup machine are alreadyknown and are used to correct the measurement values, precise valuescannot be provided.

To take a photograph of the test chart at a place where thecharacteristics of the image pickup optical system of the image pickupmachine are the same, the test chart must be moved or replaced or theimage pickup machine must be moved.

Some image pickup machines have automatic correction functions of anautomatic exposure function, an automatic gain correction function, anautomatic white balance correction function, etc. If a subject changes,a correction is made according to the setting responsive to the subject,thus a photograph of a different subject cannot be taken under the samesetup conditions.

Although the color differences between the measurement values of the R,G, and B values corresponding to the color charts on the test chart andthe theoretical R, G, and B values can be found, the spectralsensitivity characteristic of the image pickup machine as the basis ofcolor management cannot be measured.

The test chart used as a subject usually is printed matter and it isdifficult to generate black with reflectivity close to 0% and white withreflectivity close to 100%, thus the maximum value and minimum value ofmeasurement data cannot be corrected. Since the test chart is printedmatter, change with time, such as color deterioration or color change,is involved, thus measurement with high reproducibility is hard toexecute.

Only with limited types of images picked up by the image pickup machine,the color difference from any other general subject is not seen.

Only with information provided from limited types of images picked up bythe image pickup machine, a highly accurate color correction cannot bemade to the image of any other general subject.

To relate measurement data of color characteristic measurement apparatusto the images picked up by the image pickup machine, work such aspreparation of an additional correspondence table becomes necessary.

If the type of illumination light source (spectral distributioncharacteristic) changes, the data corresponding to each color chartimaged by the image pickup machine also changes. However, means foraccurately reflecting the characteristic of each illumination lightsource is not provided in related art, thus color management of theimage pickup machine containing the illumination light source is hard toaccomplish. Particularly, there is not a method of correctly measuringthe spectral sensitivity characteristic of the image pickup machine forthe reason as described above, thus if the spectral sensitivitycharacteristic of a light source, etc., is measured accurately, it doesnot lead to color management making the effective use of the spectralsensitivity characteristic.

DISCLOSURE OF THE INVENTION

According to the invention, there is provided a color characteristicmeasurement apparatus comprising a test chart as a subject, a hole beingmade in the test chart, a black box being placed on a rear face of thetest chart and formed on an inner surface in black, and a light outputsection being placed in the black box at a position where the lightoutput section can be observed through the hole from the front of thetest chart.

The test chart occupies most of the photograph taking range of an imagepickup machine as compared with the hole made in the test chart. Thus,output light of the light output section can be changed while automaticcorrection functions are fixed.

If applied light from an illumination light source of the test chart isincident on the black box through the hole, it is absorbed in the blackbox and is not reflected; it is not emitted again through the hole.Thus, output light from the light output section can be observed withoutbeing affected by the external environments.

According to the invention, there is provided a color characteristicmeasurement method comprising the steps of providing a colorcharacteristic measurement apparatus and an illumination light source,placing the color characteristic measurement apparatus and theillumination light source so that light applied from the illuminationlight source is not applied to a light output section in a black box,imaging a test chart of the color characteristic measurement apparatusby an image pickup machine, and finding a color characteristic of theimage pickup machine based on first data corresponding to the area ofthe light output section, extracted from picked up image data or seconddata provided by performing operation on the first data.

Thus, output light from the light output section not affected by theexternal illumination light source can be observed while automaticcorrection functions are fixed.

According to the invention, there is provided a picked up image datastorage medium for adding to image data provided by an image pickupmachine the gradation characteristic and the spectral sensitivitycharacteristic of the image pickup machine or the data provided byperforming operation on the gradation and spectral sensitivitycharacteristics and storing the image data.

Thus, the subject can be reproduced precisely in an image display unitwithout being affected by the color characteristic of the image pickupmachine.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an external view of an example of a color characteristicmeasurement apparatus of a first embodiment of the invention;

FIG. 2 is a sectional view of the color characteristic measurementapparatus in FIG. 1 taken on a plane perpendicular to a test chart 1containing a dashed line AB;

FIG. 3 is a sectional view to show a configuration example of a colorcharacteristic measurement apparatus of a second embodiment of theinvention;

FIG. 4 is a sectional view to show a configuration example of a colorcharacteristic measurement apparatus of a third embodiment of theinvention;

FIG. 5 is a drawing to show an example of the spectral characteristic ofthe color characteristic measurement apparatus of the third embodimentof the invention;

FIG. 6 is a sectional view to show a configuration example of a colorcharacteristic measurement apparatus of a fourth embodiment of theinvention;

FIG. 7 is a sectional view to show a configuration example of a colorcharacteristic measurement apparatus of a fifth embodiment of theinvention;

FIG. 8 is a sectional view to show a configuration example of a colorcharacteristic measurement apparatus of a sixth embodiment of theinvention;

FIG. 9 is a drawing to show image data provided when a diffuser panel isnot placed in the sixth embodiment of the invention;

FIG. 10 is a drawing to show image data provided when a diffuser panelis placed in the sixth embodiment of the invention;

FIG. 11 is a drawing to show a configuration example of a colorcharacteristic measurement apparatus of a seventh embodiment of theinvention;

FIG. 12 is a drawing to show another configuration example of the colorcharacteristic measurement apparatus of the seventh embodiment of theinvention;

FIG. 13 is a drawing to show an example of the measurement result ofspectral sensitivity containing an offset;

FIG. 14 is a drawing to show an example of the spectral sensitivitycharacteristic of an image pickup machine found by subtracting theoffset from the measurement result shown in FIG. 13;

FIGS. 15 and 16 are drawings to show configuration examples of the colorcharacteristic measurement apparatus of the seventh embodiment of theinvention, applied to the apparatus comprising a spectral filter infront of a light output section shown in FIG. 6;

FIGS. 17 and 18 are drawings to show configuration examples of the colorcharacteristic measurement apparatus of the seventh embodiment of theinvention, applied to the apparatus comprising a diffuser panel in frontof a light output section shown in FIG. 8;

FIG. 19 is a drawing to show an example of the main part of a colorcharacteristic measurement apparatus of an eighth embodiment of theinvention, wherein gray scales are placed on a test chart;

FIG. 20 is a drawing to show an example of the main part of a colorcharacteristic measurement apparatus of a ninth embodiment of theinvention, wherein color charts are placed on a test chart;

FIG. 21 is a drawing to show an example of the main part of a colorcharacteristic measurement apparatus of a tenth embodiment of theinvention;

FIG. 22 is a drawing to show an example of the main part of a colorcharacteristic measurement apparatus of an eleventh embodiment of theinvention;

FIG. 23 is a drawing to show an example of a test chart of a colorcharacteristic measurement apparatus of a fourteenth embodiment of theinvention;

FIG. 24 is a drawing to show the relationships among image data valuesoutput by an image pickup machine;

FIG. 25 is a drawing to show examples of color charts inserted into ahole in a color characteristic measurement apparatus of a fifteenthembodiment of the invention;

FIG. 26 is a drawing to show examples of image data output by an imagepickup machine;

FIG. 27 is a drawing to show an example of the found gradationcharacteristic of the image pickup machine;

FIG. 28 is a drawing to show an example of a picked up image with acolor chart inserted into the test chart;

FIG. 28 is a drawing to show another example of a picked up image with acolor chart inserted into the test chart;

FIG. 30 is a drawing to show the relationships among image data valuesoutput by the image pickup machine;

FIG. 31 is a table to list the correspondences between the wavelengthsand image data output by an image pickup machine at the wavelengths in asixteenth embodiment of the invention;

FIG. 32 is a drawing to show the spectral sensitivity characteristic ofthe image pickup machine;

FIG. 33 is a drawing to show an example applied when onesingle-wavelength light is output from a light output section;

FIG. 34 is a drawing to show another example applied when onesingle-wavelength light is output from a light output section;

FIG. 35 is a drawing to show the relationships among image data valuesoutput by the image pickup machine;

FIG. 36 is a drawing to describe a color characteristic measurementmethod of a seventeenth embodiment of the invention;

FIG. 37 is a drawing to describe correction of a spectral sensitivitycharacteristic using a gradation characteristic;

FIG. 38 is a drawing to describe the color characteristic measurementmethod of the seventeenth embodiment of the invention and is a drawingto show the gradation characteristic of an image pickup machine;

FIG. 39 is a drawing to show the spectral sensitivity characteristic ofthe image pickup machine measured;

FIG. 40 is a drawing to show the spectral sensitivity characteristic ofthe image pickup machine with the excluded effect of the gradationcharacteristic thereof;

FIG. 41 is a drawing to show data formats according to a nineteenthembodiment of the invention;

FIG. 42 is a block diagram to show a configuration example of a colorcharacteristic measurement apparatus of a twelfth embodiment of theinvention;

FIG. 43 is a drawing to describe a color management method according toa twenty-first embodiment of the invention;

FIG. 44 is a drawing to describe the color management method accordingto the twenty-first embodiment of the invention;

FIG. 45 is a drawing to describe a color characteristic measurementmethod of a twenty-second embodiment of the invention;

FIG. 46 is a drawing to show data format examples of image files in thetwenty-second embodiment of the invention;

FIG. 47 is a drawing to show data format examples of image files in atwenty-third embodiment of the invention;

FIG. 48 is a drawing to show a configuration example of a colorcharacteristic measurement apparatus in a related art; and

FIG. 49 is a drawing to show an example of a test chart of the colorcharacteristic measurement apparatus shown in FIG. 48.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the accompanying drawings, there are shown preferredembodiments of the invention.

First Embodiment

As a first embodiment of the invention, a color characteristicmeasurement apparatus for fixing the action of the automatic correctionfunction of an image pickup machine and measuring the colorcharacteristic thereof will be discussed.

FIG. 1 is an external view of an example of the color characteristicmeasurement apparatus of the first embodiment of the invention. FIG. 2is a sectional view of the color characteristic measurement apparatus inFIG. 1 taken on a plane perpendicular to a test chart 1 containing adashed line AB.

In the figures, numeral 1 denotes a test chart used as a subject,numeral 2 denotes a hole which is made in the test chart 1 and issufficiently small relative to the area of the test chart 1, numeral 3denotes a black box whose inside is painted in black, numeral 4 denotesa light output section that can be observed through the hole 2, numeral5 denotes an illumination light source having a stable colortemperature, numeral 6 denotes an image pickup machine of a testspecimen whose color characteristic is to be measured, and numeral 7denotes applied light incident on the black box 3 through the hole 2.The light output section 4 is formed of a light source in theembodiment, but may be a light emission end for emitting light from anexternal light source.

The inner walls of the black box 3 are set to sufficiently lowreflectivity and the applied light 7 incident on the black box 3 throughthe hole 2 from the outside is absorbed on the inner walls and is notreflected; it is not emitted again through the hole 2. Thus, if thelight source 4 is not provided in the black box 3 and the hole 2 isobserved from the outside, a state close to optically complete black canbe observed. Therefore, the light source 4 is placed at a position whereobservation can be made through the hole 2 from the outside, wherebyonly output light of the light source 4 not affected by the appliedlight 7 can be observed.

The image pickup machine 6 picks up the test chart 1 containing light ofthe light source 4 peeped from the hole 2. At this time, for example, ifthe image pickup machine 6 is a digital still camera, the colorcharacteristic of the image pickup machine 6 can be measured byobtaining the pixel value at the position corresponding to the lightsource 4 on the picked up image when the light source 4 is changed.

Generally, the image pickup machine 6 has automatic correction functionsof an automatic exposure function, an automatic gain correctionfunction, an automatic white balance correction function, etc. Thus, iflight source light whose characteristic changes is imaged as a subject,the automatic correction functions operate and the exposure conditions,etc., change; it is difficult to measure the precise colorcharacteristic of the image pickup machine 6 using the image data.

Then, in the embodiment, the color characteristic measurement apparatusis provided with the test chart 1 occupying most of the photographtaking range of the image pickup machine 6 as compared with the hole 2.Thus, the automatic correction functions work only for the test chart 1and can be fixed without being affected by change in the light source 4.That is, the test chart 1 and the illumination light sources 5 forapplying light to the test chart 1 as external environments are fixed,whereby the automatic correction functions can be excluded.

Using the color characteristic measurement apparatus, the light source 4can be used as a measurement object of the image pickup machine and themeasurement position can be fixed. Thus, the characteristics of theoptical system of the image pickup machine such as illuminationinconsistencies and light quantity nonuniformity depending on the imagepickup area position like a cosine fourth-power law, for example, neednot be considered. Particularly, for a consumer-oriented image pickupmachine which has various automatic correction functions, but not afunction of invalidating or fixing the automatic correction functions,subjects of various characteristics can be set without changing theautomatic correction functions.

Second embodiment

As a second embodiment of the invention, a color characteristicmeasurement apparatus for measuring the gradation characteristic of animage pickup machine will be discussed.

FIG. 3 is a sectional view to show a configuration example of the colorcharacteristic measurement apparatus of the second embodiment of theinvention. In the color characteristic measurement apparatus, anattenuator is mounted preceding a light output section 4 so that outputlight of the light output section 4 can be changed in specific lightquantity steps. According to the second embodiment, the attenuator 9 isadjusted, whereby light of any desired light quantity can be observedthrough a hole 2.

Thus, if a test chart 1 containing the hole 2 is imaged by an imagepickup machine 6 as in the first embodiment, the color characteristic ofthe image pickup machine 6 in any desired light quantity can bemeasured. That is, the light quantity of output light of the lightoutput section 4 is changed to any desired value by the attenuator 9 andthe characteristics of the image pickup machine 6 at the time aremeasured, whereby the gradation characteristic of the image pickupmachine 6 can be measured precisely and easily.

A neutral-density filter, etc., is preferred as the attenuator 9 formeasuring the gradation characteristic of the image pickup machine. Inthe second embodiment, the attenuator 9 is provided preceding the lightoutput section 4, but if the light output section 4 is an emission endof light, a similar advantage is also provided if the attenuator 9 isplaced at a point between a light source and the emission end of light.A similar advantage is also provided if the light quantity is changed bya light source with a dimmer function.

Third Embodiment

As a third embodiment of the invention, a color characteristicmeasurement apparatus for measuring the spectral sensitivitycharacteristic of an image pickup machine using a spectral light sourcewill be discussed.

FIG. 4 is a sectional view to show a configuration example of the colorcharacteristic measurement apparatus of the third embodiment of theinvention. In the color characteristic measurement apparatus, a spectrallight source 8 is attached to a light output section 4 for emitting aspectrum of output light of the light source. According to the thirdembodiment, the wavelength of light output from the spectral lightsource 8 is set, whereby spectrum of any desired wavelength can beobserved through a hole 2. The spectral light source 8 generally is madeup of a lamp such as a halogen lamp and a spectroscope.

According to the third embodiment, a test chart 1 containing the hole 2is imaged by an image pickup machine 6 as in the first embodiment,whereby the characteristics of the image pickup machine 6 relative tolight of any desired wavelength can be measured without being affectedby various automatic functions. Thus, the wavelength of light outputfrom the light output section 4 is changed by the spectral light source8 and the characteristics of the image pickup machine 6 at the time aremeasured, whereby the spectral sensitivity characteristic of the imagepickup machine 6 can be measured precisely and easily. The wavelengthmay be represented as barycentric wavelength.

If the color characteristic measurement apparatus is configured so thatoutput light of the light output section 4 can be changed in specificwavelength steps with respect to a specific wavelength range by thespectral light source 8, the spectral sensitivity characteristic of theimage pickup machine 6 can be provided with higher practicality.

If the spectral wavelength range of the spectral light source 8 is setto a visible light range, the spectral sensitivity characteristic of theimage pickup machine 6 fitted to the visual characteristics of humanbeings can be provided.

The wavelength range is set in the range of 380 nm to 780 nm, wherebythe spectral sensitivity characteristic of the image pickup machine 6can be provided matching a first-kind spectral measuring instrumentconforming to Japanese Industrial Standard JIS Z 8722, for example.

Further, if the wavelength steps are set so that half-value widths ofspectral light become equal, namely, width C in B which is one-half awave height A in FIG. 5 and wavelength step R become equal as shown in awaveform chart of FIG. 5, the wavelength components overlap almost thesame. Thus, the spectral sensitivity characteristic of the image pickupmachine 6 can be provided with less lost information and less overlappedinformation relative to the measurement wavelength range. The half-valuewidth may be represented as effective wavelength width.

Fourth Embodiment

As a fourth embodiment of the invention, a color characteristicmeasurement apparatus for measuring the spectral sensitivitycharacteristic of an image pickup machine using a spectral filter willbe discussed.

FIG. 6 is a sectional view to show a configuration example of the colorcharacteristic measurement apparatus of the fourth embodiment of theinvention. The color characteristic measurement apparatus comprises afilter 10 having a specific spectral transmission factor characteristicplaced in front of a light output section 4.

Light that can be observed through a hole 2 is only light of outputlight of the light output section 4 passing through the filter 10. Thespectral transmission factor characteristic of the filter 10 can bechanged by replacing the filter 10. Therefore, light observed throughthe hole 2 can be made light of any desired spectral distributioncharacteristic.

Fifth Embodiment

As a fifth embodiment of the invention, a color characteristicmeasurement apparatus using an external light source will be discussed.

FIG. 7 is a sectional view to show a configuration example of the colorcharacteristic measurement apparatus of the fifth embodiment of theinvention. In the figure, numeral 11 denotes an optical fiber andnumeral 12 denotes a light source unit such as a lamp house. The colorcharacteristic measurement apparatus has the light source unit 12separated from a black box 3. According to the fifth embodiment, lightof the light source unit 12 at an outside position distant from theapparatus is guided through the optical fiber 11 into the equipment andcan be measured as output light from a light output section 4. Silicaglass, etc., is preferred as a material of the optical fiber 11 ifwavelength light of 400 nm or less is to be measured.

The configuration of the color characteristic measurement apparatus isuseful if the light source is of large size as compared with the blackbox 3 or requires heat radiation. In FIG. 7, the optical fiber is shownas a typical optical waveguide device, but a similar advantage can beprovided if any other optical waveguide device is used.

Sixth Embodiment

As a sixth embodiment of the invention, a color characteristicmeasurement apparatus using a diffuser panel for decreasing ameasurement error will be discussed.

FIG. 8 is a sectional view to show a configuration example of the colorcharacteristic measurement apparatus of the sixth embodiment of theinvention. In the figure, numeral 13 denotes a diffuser panel, which isplaced in front of a light output section 4 for diffusing light.

FIG. 9 is an enlarged view of the portion of the light output section 4with respect to image data picked up by an image pickup machine 6 withthe diffuser panel 13 not placed. Generally, in the color characteristicmeasurement apparatus for packing up an image of a light source or anoptical fiber emission end, the pixel values of image data of the lightoutput section 4 vary, as shown in FIG. 9, due to the effects of changein the optical axis, the light quantity difference in minute areas ofthe light source, etc., resultantly, the measurement values contain manyerrors.

However, output light of the light source 4 can be diffused by placingthe diffuser panel 13 in front of light of the light output section 4,so that light of the light output section 4 observed through a hole 2becomes averaged light as shown in FIG. 10 with the error causesexcluded. That is, the light output section 4 observed through the hole2 can be made a uniform surface light source and measurement accuracycan be enhanced.

Seventh Embodiment

As a seventh embodiment of the invention, a color characteristicmeasurement apparatus for adding an offset to the output light quantityof a light output section 4 and measuring the spectral sensitivity of animage pickup machine will be discussed.

FIG. 11 is a drawing to show a configuration example of the colorcharacteristic measurement apparatus of the seventh embodiment of theinvention. The color characteristic measurement apparatus is the same asthat shown in FIG. 2 for emitting light from a spectral light source(not shown) through the light output section 4 except that the lightoutput section 4 is placed nearer to a hole 2 in a test chart 1 so thatillumination light sources 5 illuminate the light output section 4 in ablack box 3.

The inner walls of the black box 3 are set to sufficiently lowreflectivity and most of applied light 7 incident on the black box 3from the illumination light sources 5 is absorbed on the inner walls ofthe black box 3 and is not reflected; it is not emitted again throughthe hole 2. Therefore, an offset as much as the reflected light quantityof the applied light 7 reflected on the light output section 4 is addedto the output light quantity from the light output section 4.

FIG. 13 shows the spectral sensitivity characteristic of an image pickupmachine 6 measured by the color characteristic measurement apparatus.Offset A in the figure denotes the offset applied from the illuminationlight sources 5. After the spectral sensitivity characteristic shown inFIG. 13 is provided, the offset is subtracted therefrom, whereby thespectral sensitivity characteristic of the image pickup machine 6 isprovided as shown in FIG. 14.

The spectral sensitivity characteristic shown in FIG. 14 contains anegative component. Formerly, it was difficult to precisely measure sucha characteristic of the image pickup machine. Using the colorcharacteristic measurement apparatus, an offset is added to the outputlight quantity from the light output section 4 and the spectralsensitivity characteristic of the image pickup machine is measured,whereby precise measurement can also be made on the negative componentcontained in such a spectral sensitivity characteristic.

The offset shown in FIG. 13, offset A, is a value corresponding to thelight quantity found by observing the light output section 4 with nolight output therefrom.

FIG. 12 is a drawing to show another configuration example of the colorcharacteristic measurement apparatus of the seventh embodiment of theinvention. The color characteristic measurement apparatus is provided byadding one or more additional illumination light sources 30 to theapparatus shown in FIG. 2.

The illumination light sources 5 are placed at positions where appliedlight is not applied to the light output section 4 as in FIG. 2, whereasthe illumination light sources 30 are placed at positions where appliedlight is applied to the light output section 4, and applied light fromthe illumination light sources 30 is reflected on the light outputsection 4 and becomes an offset. Thus, the illumination intensity of atest chart is controlled by means of the illumination light sources 5and the offset can be controlled by means of the illumination lightsources 30.

FIGS. 15 to 18 are drawings to show other configuration examples of thecolor characteristic measurement apparatus of the seventh embodiment ofthe invention.

The configuration examples of the color characteristic measurementapparatus shown in FIGS. 15 and 16 are applied to the apparatuscomprising the spectral filter 10 in front of the light output section 4previously described with reference to FIG. 6. The color characteristicmeasurement apparatus shown in FIG. 15 comprises the illumination lightsources 5 for illuminating the spectral filter 10 and the apparatusshown in FIG. 16 comprises the illumination light sources 30 forilluminating the spectral filter 10 rather than the illumination lightsources 5. Thus, the color characteristic measurement apparatuscomprising the spectral filter can also measure output light to which anoffset is added.

The configuration examples of the color characteristic measurementapparatus shown in FIGS. 17 and 18 are applied to the apparatuscomprising the diffuser panel 13 in front of the light output section 4previously described with reference to FIG. 8. The color characteristicmeasurement apparatus shown in FIG. 17 comprises the illumination lightsources 5 for illuminating the diffuser panel 13 and the apparatus shownin FIG. 18 comprises the illumination light sources 30 for illuminatingthe diffuser panel 13 rather than the illumination light sources 5.Thus, the color characteristic measurement apparatus comprising thediffuser panel can also measure output light to which an offset isadded.

Eighth Embodiment

As an eighth embodiment of the invention, a color characteristicmeasurement apparatus using a gray scale for correcting a gradationcharacteristic will be discussed.

FIG. 19 is a drawing to show an example of the main part of the colorcharacteristic measurement apparatus of the eighth embodiment of theinvention; it provides a front view of a test chart 1. In FIG. 19, grayscales 14 each comprising an arrangement of color charts different inreflectivity are placed on the test chart 1.

As previously described in the first embodiment, most image pickupmachines have automatic correction functions, which include functions ofautomatically controlling the incident light quantity, the storage time,a gamma correction characteristic, setup level, knee-point, etc.,affecting the gradation characteristic of the image pickup machine 6.

Then, the gray scales 14 are placed on the test chart 1 and a hole 2 andthe gray scales 14 are imaged by the image pickup machine 6 at the sametime, whereby if any change occurs in the automatic correction functionsof the image pickup machine 6, the effects of the gradationcharacteristic correction functions of the image pickup machine 6 can becanceled out on the data in the area of the hole 2 in the picked upimage data.

That is, when the characteristic of output light from a light outputsection 4 is changed in various manners and is observed with the imagepickup machine 6, the hole 2 and the gray scales 14 are imaged by theimage pickup machine 6 at the same time, whereby the characteristics ofthe automatic correction functions concerning the gradationcharacteristic that the image pickup machine 6 has at each observationtime are found from the data corresponding to the color charts differentin reflectivity in the gray scales 14.

Thus, correction processing can be easily performed for canceling outthe effects of the gradation characteristic correction functions of theimage pickup machine 6 on the data in the area of the light outputsection 4 in the picked up image data; precise measurement can be madewith the automatic correction function effects excluded.

If the gray scales 14 each consisting of a larger number of color chartsdifferent in reflectivity are placed on the test chart 1, more precisecharacteristics of the automatic correction functions can be provided.However, if one color chart is placed, the characteristics of theautomatic correction functions concerning the gradation characteristiccan be provided.

Ninth Embodiment

As a ninth embodiment of the invention, a color characteristicmeasurement apparatus using color charts for correcting a colorcharacteristic will be discussed.

FIG. 20 is a drawing to show an example of the main part of the colorcharacteristic measurement apparatus of the ninth embodiment of theinvention; it provides a front view of a test chart 1. In FIG. 20, colorcharts 15 different in chromaticity are placed on the test chart 1.

Most image pickup machines have automatic correction functions aspreviously described in the first embodiment and may comprise automaticcorrection functions concerning a color characteristic such as blackbalance correction, white balance correction, and color matrixcorrection.

Then, the color charts 15 are placed on the test chart 1 and a hole 2and the color charts 15 are imaged by the image pickup machine 6 at thesame time, whereby if any change occurs in the automatic correctionfunctions of the image pickup machine 6, the effects of the colorcharacteristic correction functions of the image pickup machine 6 can becanceled out on the data in the area of the hole 2 in the picked upimage data.

That is, when the characteristic of output light from a light outputsection 4 is changed in various manners and is observed with the imagepickup machine 6, the hole 2 and the color charts 15 are imaged by theimage pickup machine 6 at the same time, whereby the characteristics ofthe automatic correction functions concerning the color characteristicthat the image pickup machine 6 has at each observation time are foundfrom the data corresponding to the color charts 15 different inchromaticity.

Thus, correction processing can be easily performed for canceling outthe effects of the color characteristic correction functions of theimage pickup machine 6 on the data in the area of the light outputsection 4 in the picked up image data; precise measurement can be madewith the automatic correction function effects excluded.

If a larger number of the color charts 15 different in chromaticity areplaced on the test chart 1, more precise characteristics of theautomatic correction functions can be provided. However, if one colorchart is placed, the characteristics of the automatic correctionfunctions concerning the color characteristic can be provided.

Tenth Embodiment

As a tenth embodiment of the invention, a color characteristicmeasurement apparatus for precisely measuring the gradationcharacteristic in a low-brightness area will be discussed.

FIG. 21 is a drawing to show an example of the main part of the colorcharacteristic measurement apparatus of the tenth embodiment of theinvention; it provides a front view of a test chart 1. In FIG. 21, inaddition to a hole 2, two holes 16 are made in the test chart 1. Theseholes 16 are of sizes and are made at positions such that output lightfrom a light output section 4 is not observed on an image pickup machine6 through the holes 16 and that light from an illumination light source5 is not applied to the light output section 4 through the holes 16.

The holes 16 are made, whereby an optically almost complete blackportion in a black box 3, namely, black with reflectivity close to 0%can be observed through the holes 16, so that zero-level correction onthe test chart 1 and the light source 4 can be made. The hole 16 isprovided as a black color chart of the gray scale previously describedin the eighth embodiment, whereby a precise gradation characteristic canbe provided particularly concerning a low-brightness area.

Eleventh Embodiment

As an eleventh embodiment of the invention, a color characteristicmeasurement apparatus for precisely measuring the gradationcharacteristic in a high-brightness area will be discussed.

FIG. 22 is a drawing to show an example of the main part of the colorcharacteristic measurement apparatus of the eleventh embodiment of theinvention; it provides a front view of a test chart 1. In FIG. 22,reference white color charts 17 are placed on the test chart 1 in theproximity of a hole 2 made therein.

When the test chart 1 is imaged by an image pickup machine 6 and a lightoutput section 4 is changed in various manners, if the reflectivities ofother color charts of the test chart 1 and a background are set so thatthe image data corresponding to the reference white color charts 17becomes almost the maximum in the dynamic range of the image pickupmachine 6 and if output light of the light output section 4 is changedso that the image data in the area of the light output section 4observed through the hole 2 becomes the maximum in a range not exceedingthe image data in the reference white areas, it is made possible toexecute high-resolution measurement making the effective use of thedynamic range of the image pickup machine 6 in which image data is notsaturated with respect to high-brightness input.

If the image pickup machine 6 has channels for a number of colors,output light of the light output section 4 may be changed so that imagedata is not saturated with respect to any channels.

To set the image pickup machine 6 of the type wherein the automaticcorrection function state cannot be set from the outside so that theimage data in the reference white areas becomes almost the maximum inthe dynamic range of the image pickup machine 6, a method of placing awhite or black flat plate in the surroundings of the test chart 1 andchanging the image pickup view angle of the image pickup machine 6 orthe like is available; placement of the reference white color charts 17in the proximity of the hole 2 is also effective for the method.

As another effect of placing the reference white color charts 17 in theproximity of the hole 2 in the test chart 1, when variouscharacteristics based on the light source 4 observed through the hole 2are measured, change in the image data in the reference white areas inthe proximity of the hole 2 can be observed at the same time, so that itis made possible to detect delicate change in the gradationcharacteristic particularly in a high-brightness area and correct theabove-mentioned various characteristics in response to the change.

Twelfth Embodiment

As a twelfth embodiment of the invention, a color characteristicmeasurement method of an image pickup machine using the above-describedcolor characteristic measurement apparatus will be discussed.

First, to image a test chart 1 by the image pickup machine 6, light isapplied to the test chart 1 from the illumination light sources 5. Atthis time, light is also applied to the inside of the black box 3through the hole 2 from the illumination light sources 5. Theapplication range of the applied light 7 is determined by the size ofthe hole 2 and the positions of the illumination light sources 5. Then,the illumination light sources 5 and the test chart 1 are placed asshown in FIG. 1 so as not to apply light to the light output section 4observed through the hole 2 directly from the illumination light sources5, and the test chart 1 containing output light of the light outputsection 4 oberved through the hole 2 is imaged by the image pickupmachine 6.

If the image pickup machine 6 is, for example, a digital still camera,data corresponding to the area of the light output section 4 can beprovided from the image data output after an image is picked up. This isfirst data. Color characteristic measurement of the image pickup machine6 can be executed by observing the first data.

The image pickup machine 6 is connected to, for example, a personalcomputer, etc., and application software, etc., is used to input imagedata from the image pickup machine 6 to the personal computer, then thedata corresponding to the light output section 4 can also be providedfrom the input image data. This is second data.

Generally, the image data input to the personal computer is provided byperforming gradation characteristic conversion operation, color spaceconversion operation, operation for making good color considering thevisual characteristics of human beings, or the like on the first data.Thus, color characteristic measurement of the image pickup machine 6containing the application software can be executed by observing thesecond data.

The manufacturers or dealers of the image pickup machines 6 oftenmanufacture and sell the image pickup machine 6 and application softwarein combination, in which case color characteristic measurement of theimage pickup machine 6 can be executed based on the first data and inaddition, comprehensive color characteristic measurement of the imagepickup machine 6 containing the characteristics of the applicationsoftware, etc., can also be executed based on the second data.

The application software may be called any other representation such asdriver software. If application software, etc., for inputting image datafrom the image pickup machine 6 to any other machine or system andapplication software, etc., for performing various conversion operationson the input image data to prepare the second data are separate softwareproducts rather than one piece, a similar advantage is also provided, ofcourse.

Thirteenth Embodiment

As a thirteenth embodiment of the invention, a color characteristicmeasurement method using the color characteristic measurement apparatuspreviously described with reference to FIG. 20 with the color charts 15placed on the test chart 1 as a subject of an image pickup image 6 willbe discussed. The first or second data provided by the method of thetwelfth embodiment described above is corrected from color change in theportions of the color charts 15 in the image data picked up by the imagepickup machine 6.

According to the method of the thirteenth embodiment, if the colorcharacteristic is changed due to the effects of automatic correctionfunctions, etc., it can be corrected to provide the first or seconddata.

Fourteenth Embodiment

As a fourteenth embodiment of the invention, a color characteristicmeasurement method using the above-described color characteristicmeasurement apparatus for measuring the precise graduationcharacteristic of an image pickup machine 6 will be discussed.

If the above-described color characteristic measurement apparatus isused, the automatic correction functions of the image pickup machine 6work only for the test chart 1 and are not affected by change in outputlight of the light output section 4. However, the automatic functions ofthe image pickup machine 6, for example, the automatic exposure controlfunction may work because of change in the illumination intensity of theillumination light source 5 illuminating the test chart 1. If the imagepickup machine 6 is a digital camera, etc., often the exposure controloperation is repeated within a short time each time an image is pickedup, thus the iris, electronic shutter speed, signal processing gain, andthe like are not necessarily the same whenever an image is picked up.

Change in the illumination intensity of the illumination light source 5can be suppressed by using a stabilized power supply for supply power tothe illumination light source 5. Change of the automatic functions ofthe image pickup machine 6 is minute because the subject is the sameexcept for output light through the hole 2. However, to measure theprecise gradation characteristic of the image pickup machine 6, theeffect of the minute change needs also to be corrected.

As an example, a case will be examined where the light quantity ofoutput light of the light output section 4 is changed continuously orgradually from 0% to 100% of the maximum light quantity. The lightoutput section 4 does not output light and light entered through thehole 2 is not output either through the hole 2 to the outside, wherebythe light quantity of 0% can be realized.

Then, the output light quantity of the light output section 4 isadjusted in the range of 0% to 100% and the test chart 1 is imaged bythe image pickup machine 6 in each adjusted light quantity. At thistime, as shown in FIG. 23, the test chart 1 is provided with gray scales14 each consisting of color charts 14C different in reflectivity and theimage pickup machine 6 also images the color charts 14C at the same timeas output light from the light output section 4.

When the automatic functions of the image pickup machine 6 do notchange, if the output light quantity of the light output section 4 ischanged gradually and an image is picked up each time, the image datavalues of the gray scales 14 become the same in every image. However, ifthe image data values of the gray scales 14 change for some factor, theimage data values of the light output section 4, namely, the hole 2 formeasuring the gradation characteristic of the image pickup machine 6also change likewise, thus the precise gradation characteristic cannotbe provided.

Then, a chart applied when the output light quantity of the light outputsection 4 is adjusted to a specific light quantity (for example, 50% ofthe maximum light quantity) is adopted as a reference chart and theimage data values of the gray scale 14 provided when the output lightquantity is changed are compared with those of the gray scale 14 of thereference chart. If they differ, the image data value of the lightoutput section 4 is corrected linearly as much as the image data valuedifference between the gray scales 14.

Let the image data values of the color charts 14C imaged with outputlight of the light output section 4 set to one light quantity be Y0, Y1,. . . , Y14 and Y15 and the image data value of the light output section4 at the time be Xi. Assume that the relation between the image datavalues Y0 to Y15 of the color charts 14C and the image data value Xisatisfies the following expression (1):

Y 0, Y 1, . . . <Yi<Xi<Yi+1 . . . , Y 14, Y 15  (1)

Let the image data values of the color charts 14C on the reference chartbe Ystd0, Ystd1, . . . , Ystd14, and Ystd15.

At this time, if the image data value Yi or Yi+1 of the color chartdiffers from the image data value Ystdi or Ystdi+1 of the correspondingcolor chart 14C on the reference chart (Yi≠Ystdi or Yi+1≠Ystdi+1), theimage data value Xi is corrected according to the following expression,namely, post-corrected image data value X′i is found according to thefollowing expression (2):

X′i=(Xi−Yi)(Ystdi+1−Ystdi)/(Yi+1−Yi)+Ystdi  (2)

The correction shown in expression (2) will be discussed with referenceto FIG. 24, which is a drawing to show the relationships among the imagedata values. The image data values Yi, Xi, and Yi+1 provided when thelight quantity is changed and the image data values Ystdi+1 and Ystdi ofthe reference chart are shown. In the image data of the reference chart,the true value of the image data Xi should be at the position of X′ishown in FIG. 24. Therefore, the true value of the image data Xi can becalculated according to the above-mentioned expression (2).

When output data of the image pickup machine 6 is R, G, and B, if theimage data values of the color charts 14C change from those of thereference chart, a similar correction is made to R, G, and B data,whereby the true values of the image data in each image can be providedand the precise gradation characteristic of the image pickup machine 6can be measured.

If the correction is made to the first data provided by the method ofthe twelfth embodiment, the gradation characteristic of the image pickupmachine 6 can be found; if the correction is made to the second data,the comprehensive gradation characteristic of the image pickup machine 6also containing application software can be found.

Fifteenth Embodiment

As a fifteenth embodiment of the invention, a color characteristicmeasurement method using the above-described color characteristicmeasurement apparatus for imaging a color chart inserted into the hole 2in the test chart 1 by an image pickup machine 6 and measuring theprecise gradation characteristic of the image pickup machine 6 will bediscussed.

As in the fourteenth embodiment, the automatic correction functions ofthe image pickup machine 6 work only for the test chart 1 and are notaffected by change in the color chart inserted into the hole 2, but maywork because of the effect of disturbance or each time an image ispicked up. Thus, to measure the precise gradation characteristic of theimage pickup machine 6, the effects need to be corrected.

As an example, the reflectivities of color charts 2C are set to 0.0%,2.0%, 4.0%, 6.0%, 8.0%, 10.3%, 14.7%, 19.8%, 25.8%, 32.5%, 39.9%, 48.1%,57.0%, 66.6.%, 77.0%, and 88.1%. If it is difficult to prepare the colorchart 2C of reflectivity 0.0%, no color chart is inserted into the hole2 in the test chart 1 in a state in which light is not emitted from thelight output section 4 and light entered through the hole 2 is notoutput again through the hole 2 to the outside, whereby the color chart2C of reflectivity 0% can be realized.

The test chart 1 used is similar to that in FIG. 23. The color charts 2Cdifferent in reflectivity are placed in the hole 2 one at a time inorder and an image is picked up by the image pickup machine 6. FIG. 25shows the color charts 2C different in reflectivity each inserted intothe hole 2 in the test chart 1.

The color charts 2C are inserted into the hole 2 in the test chart 1 oneat a time in order and the test chart 1 is imaged by the image pickupmachine 6 under the photograph taking conditions shown in FIG. 2. Thepixel values of the color charts 2C in the picked up images are found,whereby the gradation characteristic of the image pickup machine 6 canbe measured. For example, when output data of the image pickup machine 6is R, G, and B and output data of the color charts 2C different inreflectivity is provided as shown in FIG. 26, the gradationcharacteristic of the image pickup machine 6 of the test specimen can berepresented as shown in FIG. 27.

FIG. 28 shows an image picked up by the image pickup machine 6 with thecolor chart 2C of reflectivity 25.8% inserted into the test chart 1.FIG. 29 shows an image picked up by the image pickup machine 6 with thecolor chart 2C of reflectivity 77.0% inserted into the test chart 1. Tomeasure the gradation characteristic of the image pickup machine 6, asmany images as the number of the color charts 2C different inreflectivity are picked up as images shown in FIGS. 28 and 29.

Now, assume that the image shown in FIG. 28 is adopted as a referencechart. Gray scales 14 in FIG. 28 are each provided with color charts 14Cdifferent in reflectivity. The color charts 14C on the gray scales 14may or may not be of the same reflectivities as the color charts 2Cshown in FIG. 25.

When the automatic functions of the image pickup machine 6 do notchange, if the color charts 2C different in reflectivity are insertedinto the hole 2 in the test chart 1 one at a time in order and an imageis picked up by the image pickup machine 6, the image data values of thegray scales 14 become the same in every image. However, if the imagedata values of the color charts of the gray scales 14 change for somefactor, the image data values of the color charts 2C for measuring thegradation characteristic of the image pickup machine 6 also changelikewise, thus the precise gradation characteristic cannot be provided.

If the provided image data values of the color charts of the gray scales14 differ from the image data values of the gray scales 14 of thereference chart, the image data value of the color chart 2C is correctedlinearly as much as the image data value difference.

Let the image data values of the color charts 14C of the gray scales 14imaged with the color chart 2C of one reflectivity inserted into thehole 2 in the test chart 1 as shown in FIG. 29 be Y0, Y1, . . . , Y14and Y15 and the image data value of the color chart 2C at the time beXi. Assume that the relation between the image data value of the colorchart 2C and the image data values of the color charts 14C of the grayscales 14 in FIG. 29 satisifes the following expression (3):

Y 0, Y 1, . . . <Yi<Xi<Yi+1 . . . , Y 14, Y 15  (3)

Let the image data values of the color charts 14C on the reference chartshown in FIG. 28 be Ystd0, Ystd1, . . . , Ystd14, and Ystd15.

When the image data value Yi or Yi+1 of the color chart 14C differs fromthe image data value Ystdi or Ystdi+1 of the corresponding color chart14C on the reference chart (Yi≠Ystdi or Yi+1≠Ystdi+1), the image datavalue Xi is corrected according to the following expression: (Assumethat post-corrected image data value is X′i.)

X′i=(Xi−Yi)(Ystdi+1−Ystdi)/(Yi+1−Yi)+Ystdi  (4)

The correction shown in expression (4) will be discussed with referenceto FIG. 30, which is a drawing to show the relationships among the imagedata values. The relationships among the image data values Yi, Xi, andYi+1 shown in FIG. 28 are as shown in FIG. 30. When the values Ystdi+1and Ystdi of the reference chart are the values shown in FIG. 30, thetrue value of the image data Xi should be at the position of X′i shownin FIG. 30. Therefore, the true value of the image data Xi can becalculated according to the above-mentioned expression (4).

When output data of the image pickup machine 6 is R, G, and B, a similarcorrection is made to each of R data, G data, and B data, whereby thetrue value of the image data of the color chart 2C in each image can beprovided and the precise gradation characteristic of the image pickupmachine 6 can be measured.

The embodiment uses the image with the color chart 2C of reflectivity25.8% inserted in the hole 2 as the reference chart, but if an imagewith any other color chart 2C inserted in the hole 2 is used as thereference chart, a similar advantage can be provided, needless to say.

If the correction is made to the first data provided by the method ofthe twelfth embodiment, the gradation characteristic of the image pickupmachine 6 can be found; if the correction is made to the second data,the comprehensive gradation characteristic of the image pickup machine 6also containing application software can be found.

Sixteenth Embodiment

As a sixteenth embodiment of the invention, a color characteristicmeasurement method using the above-described color characteristicmeasurement apparatus for measuring the precise spectral sensitivitycharacteristic of an image pickup machine 6 will be discussed.

If the above-described color characteristic measurement apparatus isused, the automatic correction functions of the image pickup machine 6work only for the test chart 1 and are not affected by change in thelight output section 4, but may work because of the effect ofdisturbance or each time an image is picked up. To measure the precisespectral sensitivity characteristic of the image pickup machine 6, theeffects need to be corrected.

In the above-described color characteristic measurement apparatus,output light from the light output section 4 is changed in specificwavelength steps in a specific wavelength range and the test chart 1 isimaged by the image pickup machine 6. In the picked up image, the pixelvalues of the light output section 4 are found for each specificwavelength, whereby the spectral sensitivity characteristic of the imagepickup machine 6 can be measured. For example, when output data of theimage pickup machine 6 is R, G, and B and output data at the wavelengthsis provided as shown in FIG. 31, the spectral sensitivity characteristicof the image pickup machine 6 of the test specimen can be represented asshown in FIG. 32.

As an example, the wavelengths of output light of the light outputsection 4 are 380 nm, 385 nm, 390 nm, . . . , 770 nm, 775 nm, and 780nm. FIG. 33 shows an image picked up by the image pickup machine 6 whensingle-color light of wavelength 580 nm is emitted. In FIG. 33, an imageof the light output section 4 in the hole 2 is picked up. FIG. 34 showsan image picked up when light of wavelength λ nm is emitted. To measurethe color characteristic of the image pickup machine 6, as many imagesas the number of the different wavelengths are picked up as images shownin FIGS. 33 and 34. If an image is thus picked up in 5-nm steps in therange of 380 nm to 780 nm, 81 images are picked up in total.

Now, assume that the image, shown in FIG. 33, picked up when thewavelength of output light through the hole 2 is 580 nm is adopted as areference chart. Gray scales 14 in FIG. 33 are each provided with colorcharts 14C different in reflectivity.

When the automatic functions of the image pickup machine 6 do notchange, if the wavelength of output light from the light output section4 is changed and an image is picked up by the image pickup machine 6each time, the image data values of the color charts 14C of the grayscales 14 are the same in every image. However, if the image data valuesof the color charts 14C of the gray scales 14 change for some factor,the image data values of the light output section 4 for measuring thespectral sensitivity characteristic of the image pickup machine 6 alsochange likewise, thus the precise color characteristic cannot beprovided.

If the provided image data values of the color charts of the gray scales14 differ from the image data values of the gray scales 14 of thereference chart, the image data value of the light output section 4 iscorrected linearly as much as the image data value difference.

Let the image data values of the color charts 14C of the gray scales 14of an image picked up when the wavelength of one output light of thelight output section 4 is λ be Y0, Y1, . . . , Y14 and Y15, as shown inFIG. 34, and the image data value of the light output section 4 be Xλ.Assume that in FIG. 34, the relation between the image data value of thelight output section 4 and the image data values of the color charts 14Cof the gray scales 14 satisfies the following expression (5):

Y 0, Y 1, . . . <Yi<Xλ<Yi+1 . . . , Y 14, Y 15  (5)

Let the image data values of the color charts 14C of the gray scales 14on the reference chart be Ystd0, Ystd1, . . . , Ystd14, and Ystd15, asshown in FIG. 33.

At this time, if the image data value Yi or Yi+1 of the color chartdiffers from the image data value Ystdi or Ystdi+1 of the correspondingcolor chart on the reference chart (Yi≠Ystdi or Yi+1≠Ystdi+1), the imagedata value Xλ is corrected according to the following expression (6):(Assume that post-corrected image data value is X′λ.)

X′λ=(Xλ−Yi)(Ystdi+1−Ystdi)/(Yi+1−Yi)+Ystdi  (6)

FIG. 35 shows the relationships among the image data values. Thecorrection shown in expression (6) will be discussed with reference toFIG. 35. The relationships among the image data values Yi, Xλ, and Yi+1shown in FIG. 34 are as shown in FIG. 35. When the values Ystdi+1 andYstdi of the reference chart are the values shown in FIG. 35, the truevalue of the image data Xλ should be at the position of X′λ shown inFIG. 35. Therefore, the true value of the image data Xλ can becalculated according to the above-mentioned expression (6).

When output data of the image pickup machine 6 is R, G, and B, a similarcorrection is made to each of R data, G data, and B data, whereby thetrue value of the image data of the light output section 4 in each imagecan be provided and the precise color characteristic of the image pickupmachine 6 can be measured.

The embodiment uses the image picked up when the wavelength of outputlight of the light output section 4 is 580 nm as the reference chart,but if an image picked up when the wavelength is any other than 580 nmor an image picked up with a color chart of any reflectivity inserted inthe hole 2 in the test chart shown in the fifteenth embodiment is usedas the reference chart and the correction based on the above-mentionedexpression (6) is made, a similar advantage can be provided, needless tosay.

If the correction is made to the first data provided by the method ofthe twelfth embodiment, the color characteristic of the image pickupmachine 6 can be found; if the correction is made to the second data,the comprehensive color characteristic of the image pickup machine 6also containing application software can be found.

Seventeenth Embodiment

As a seventeenth embodiment of the invention, a color characteristicmeasurement method using the above-described color characteristicmeasurement apparatus for measuring the spectral sensitivitycharacteristic of an image pickup machine 6 from which the effect of thegradation characteristic of the image pickup machine 6 is excluded willbe discussed.

FIG. 36 is a drawing to an example of the gradation characteristic of animage pickup machine, wherein first data is indicated by the solid lineand second data is indicated by the dashed line. As indicated by thesolid line in the figure, often the gradation characteristic of theimage pickup machine 6 is not linear; it is corrected by acharacteristic inverse to the gradation characteristic, whereby a linearcharacteristic as indicated by the dashed line in the figure isprovided.

FIG. 37 is a drawing to show a correction example. It shows a spectralsensitivity characteristic. If the gradation characteristic is notlinear, namely, the spectral sensitivity characteristic having acharacteristic as indicated by the solid line in FIG. 36 becomes acharacteristic as indicated by the solid line in FIG. 37. However, it iscorrected by the above-mentioned gradation characteristic, whereby thelinear spectral sensitivity characteristic indicated by the dashed linein FIG. 37 can be provided.

The correction will be discussed in more detail. FIG. 38 shows thegradation characteristic of the image pickup machine 6 measured by themeasurement method previously described in the fifteenth embodiment.FIG. 39 shows the spectral sensitivity characteristic of the imagepickup machine 6 measured by the measurement method previously describedin the sixteenth embodiment. The input/output characteristic of theimage pickup machine is nonlinear and the corrected linearcharacteristic is indicated by dashed line D in FIG. 38. Spectralsensitivity measurement is made using output data of the image pickupmachine 6 and thus is affected by the gradation characteristic of theimage pickup machine 6. Then, to find a linear spectral sensitivitycharacteristic of the image pickup machine 6 with the excluded effect ofthe gradation characteristic thereof, the following correction needs tobe made:

Gradation characteristic of the image pickup machine 6 shown in FIG. 38,Yc, is represented by the following expression:

Yc=fc(Li)  (7)

where c: R, G, B

fc(Li): Function of line indicated by solid line in FIG. 38

Li: Luminance of color chart at imaging time

Letting the measured spectral sensitivity characteristic in FIG. 39 beSc(λ), linear spectral sensitivity characteristic with the excludedeffect of the gradation characteristic of the image pickup machine,Sc′(λ), is found by the following expression:

Sc′(λ)=fc ⁻¹(Sc(λ))  (8)

where c: R, G, B

Thus, a correction is made to each of R, G, and B image data provided inthe sixteenth embodiment as indicated in the following expression:

Sc′(λ)=kfc ⁻¹(X′λ−X′0)  (9)

where k: Coefficient to set the maximum value of Sc(λ) to 100%

X′0: Image data value of color chart having the lowest luminance valueprovided in the fifteenth embodiment

The linear spectral sensitivity characteristic Sc′(λ) is provided bymaking the correction according to the expression (9).

To use the spectral sensitivity characteristic for color management ofcolor space conversion, etc., it is assumed that the addition law incolor metrology is true as a rule. Thus, the advantage in that thelinear characteristic is provided as described above is large.

If the correction is made to the first data provided by the method ofthe twelfth embodiment, the linear spectral sensitivity characteristicof the image pickup machine 6 can be found; if the correction is made tothe second data, the linear color characteristic of a system alsocontaining application software can be found.

In the embodiment, the gradation characteristic measured with colorchart 2C inserted (fifteenth embodiment) has been described, but theseventeenth embodiment is also applied to the gradation characteristicmeasured with the output light quantity of light output section 4changed (fourteenth embodiment).

Measuring the precise spectral sensitivity characteristic of the imagepickup machine requires that the light quantity of the spectral lightsource be constant and that the gradation characteristic of the imagepickup machine be linear. Thus, gradation characteristic correction ismade and if the light quantity for the spectrum wavelength is notconstant, a similar correction is made using the light quantitycharacteristic relative to the wavelength, whereby the precise spectralsensitivity characteristic of the image pickup machine can be found.

Eighteenth Embodiment

The above-described color characteristic measurement apparatus can beused to find the gradation characteristic and spectral sensitivitycharacteristic of an image pickup machine 6 by the color characteristicmeasurement method of any of the twelfth to seventeenth embodiments.

Then, the gradation and spectral sensitivity characteristics areprovided in a one-to-one correspondence with the image pickup machines 6and are managed, whereby if the image pickup machines 6 are machinesstable in aging, for example, good use of the gradation and spectralsensitivity characteristics can be made without measuring the colorcharacteristic of each image pickup machine each time a photograph istaken.

To connect the image pickup machine 6 to any other machine to form asystem, highly accurate color management in the system is enabledbecause the gradation and spectral sensitivity characteristics areobvious.

It is described that the gradation and spectral sensitivitycharacteristics are provided in a one-to-one correspondence with theimage pickup machines 6 and are managed. However, if data provided byperforming operation on from the gradation characteristic, such as setuplevel, gamma correction characteristic, and knee-point, and dataprovided by performing operation on the spectral sensitivitycharacteristic, such as wavelength at which sensitivity becomes themaximum, half-value wavelength width, and matrix coefficient forconversion to general color space such as XYZ color system, are providedin a one-to-one correspondence with the image pickup machines 6 and aremanaged in place of or together with the gradation and spectralsensitivity characteristics, it may be advantageous in the point of thedata amount or the computation time of the apparatus for receiving animage from the image pickup machine 6 and processing the image; the mainpurpose and advantages are similar to those described above.

Nineteenth Embodiment

Next, FIG. 41 shows the data formats for adding the gradation andspectral sensitivity characteristics of an image pickup machine 6 toimage data picked up by the image pickup machine 6.

In FIG. 41, the data format in Example 1 comprises the gradationcharacteristic added to image data; the data format in Example 2comprises the spectral sensitivity characteristic added to image data;and the data format in Example 3 comprises the gradation and spectralsensitivity characteristics added to image data.

By using such a data format, what gradation characteristic or spectralsensitivity characteristic the image pickup machine picking up theprovided image data has becomes obvious; highly accurate colormanagement is enabled for each image data.

In the nineteenth embodiment, the data format examples for adding bothor either of the gradation and spectral sensitivity characteristics toimage data are shown. However, as previously described in the eighteenthembodiment, if data provided by performing operation on the gradationcharacteristic and data provided by performing operation on the spectralsensitivity characteristic are added in place of or together with thegradation and spectral sensitivity characteristics, it may beadvantageous in the point of the data amount or the computation time ofthe apparatus for receiving an image from the image pickup machine 6 andprocessing the image; the main purpose and advantages are similar tothose described above.

In the nineteenth embodiment, the data format examples for adding eachcharacteristic to the top of image data are shown. However, a similaradvantage is provided regardless of where the added characteristic isplaced in the image data, needless to say.

Twentieth Embodiment

FIG. 42 is a block diagram to show a configuration example of a colorcharacteristic measurement apparatus of a twelfth embodiment of theinvention. In the figures numeral 18 denotes a storage unit installed inan image pickup machine 6.

The storage unit 18 stores the gradation characteristic or spectralsensitivity characteristic of the image pickup machine 6 found using thecolor characteristic measurement apparatus by the above-describedmeasurement method. According to such a configuration, thecorrespondence between the image pickup machines 6 and eachcharacteristic previously described in the eighteenth embodiment becomesclearer and in addition, the data in the nineteenth embodiment can alsobe prepared easily.

A similar advantage is provided regardless of the type of storage unit18, such as semiconductor memory, a magnetic disk unit, or an opticaldisk unit.

Twenty-first Embodiment

Let the spectral sensitivity characteristic of an image pickup machinehaving n channels (n is a natural number) found using theabove-described color characteristic measurement apparatus by theabove-described measurement method be Cn(λ). FIG. 43 shows Cn(λ) (n=1,2, 3 corresponding to R, G, B respectively) of the image pickup machinehaving three channels of R, G, and B. Let the spectral distributioncharacteristic of an illumination light source when a subject is imagedby the image pickup machine be L(λ) as shown in FIG. 44.

The color characteristic of the image pickup machine 6 can be shown bythe spectral sensitivity characteristic Cn(λ) (n=1, 2, 3) and thespectral distribution characteristic of the illumination light source,L(λ). The characteristic data is added to image data or image data isrelated to the characteristic data, whereby color management can beexecuted with the image data provided in a one-to-one correspondencewith the color characteristics of the image pickup machines picking upthe image data.

Further, color management of color space conversion, etc., can beexecuted according to the spectral characteristics of three channelsprovided by multiplying Cn(λ) by L(λ).

In the twenty-first embodiment, the color management method according tothe spectral characteristic is described. However, if color managementis executed according to data provided by performing operation on thespectral characteristic, such as wavelength at which the spectralcharacteristic value becomes the maximum, half-value wavelength width,and matrix coefficient for conversion to general color space such as XYZcolor system, the main purpose and advantages are similar to thosedescribed above.

In the twenty-first embodiment, the image pickup machine having threecolor channels is described, but a similar advantage is provided if thenumber of color channels is changed. That is, with the image pickupmachine having n color channels, n+1 characteristic data piecesconsisting of spectral sensitivity characteristic Cl(λ) to Cn(λ) and thespectral distribution characteristic of the illumination light source,L(λ), are provided and n characteristic data pieces are provided bymultiplying Cn(λ) by L(λ).

Twenty-second Embodiment

In a twenty-second embodiment of the invention, a method of compensatingfor the difference between the gradation characteristic of an imagepickup machine and that of an image output unit and the data format ofan image file will be discussed.

FIG. 45A is a drawing to show a configuration example of a system foroutputting image data picked up by an image pickup machine 6 to an imageoutput unit 20. FIGS. 45A and 45B are drawings to show examples of ycharacteristics of the image output unit 20 and the image pickup machine6 respectively.

The data of an image picked up by the image pickup machine 6 istransferred to the image output unit 20 as an image file for each imagein serial/parallel communication over a cable 21 directly connecting theimage pickup machine 6 and the image output unit 20 or via infraredcommunication 22, a storage medium 23, or the like.

The gradation characteristic of the image pickup machine 6 can berepresented by γ coefficient γc as in the following expression:

Sout=(Lin)^(1/γc)  (10)

where Sout is a signal level output from the image pickup machine 6 andLin is a luminance level of a subject. The gradation characteristic ofthe image output unit 20 can be represented by γ coefficient γD as inthe following expression:

Lout=(Sin)^(γD)  (11)

where Lout is light emission luminance and Sin is an input signal levelto the image output unit 20.

For the gradation characteristic of a subject and that of an outputimage of the image output unit 20 to match, namely, to set Lin=Lout, theγ coefficient γc of the image pickup machine 6 needs to equal the γcoefficient γD of the image output unit 20. Thus, when γc≠γD, if k·γc isset equal to γD by multiplying γc by coefficient k, Lin=Lout results.The coefficient k is added to the image data provided by the imagepickup machine 6. FIG. 46 shows data format examples of image files. Thedata format in Example 1 comprises the coefficient k added to the top ofimage data. The data format in Example 2 comprises the coefficient k andthe gradation characteristic of the image pickup machine 6 preceding thetop of image data. Using such image data, the gradation characteristicdifference between the image pickup machine 6 and the image output unit20 can be compensated on a personal computer, etc., for example.

The data formats shown in FIG. 46 are examples and a similar effect isprovided if the coefficient k is added to any part of image data,needless to say.

In the embodiment, a personal computer system containing a monitor isshown an example of the image output unit 20 in FIG. 45. However, theembodiment is also applied if the image output unit 20 is a printer, aprojector, etc., rather than the monitor.

The gradation characteristic of the image pickup machine 6 can be foundby the gradation characteristic measurement method previously describedin the fourteenth or fifteenth embodiment. Using the gradationcharacteristic measured by the method described in the fourteenth orfifteenth embodiment, the precise coefficient k can be calculated andthe gradation characteristic difference between the image pickup machine6 and the image output unit 20 can be eliminated.

Twenty-third Embodiment

In a twenty-third embodiment of the invention, a method of compensatingfor a color reproduction error and the image file data formats will bediscussed.

FIG. 45 is a drawing to show that a subject is imaged by image pickupmachine 6 as previously mentioned in the twenty-second embodiment.Assume that the image pickup machine 6 has an image pickupcharacteristic fitted to the color space of image output unit 20; forexample, if the image output unit 20 is an NTSC monitor, the imagepickup machine 6 has NTSC image pickup characteristic or if the imageoutput unit 20 has an sRGB space, the image pickup machine 6 has animage pickup characteristic fitted to the sRGB space. A color chart of aknown spectral distribution characteristic ρ(λ) is placed on a testchart 1. If an illumination light source 5 is reference white defined inthe sRGB space, the signals of the color chart provided from the imagepickup machine 6 are Rs, Gs, and Bs.

The signals of the color chart, Rc, Gc, and Bc, provided underillumination of spectral distribution characteristic L(λ) by the imagepickup machine 6 having spectral distribution characteristic R(λ), G(λ),B(λ) are represented by the following expressions:

Rc=∫ρ(λ)×R(λ)×L(λ)dλ  (12)

Gc=∫ρ(λ)×G(λ)×L(λ)dλ  (13)

Bc=∫ρ(λ)×B(λ)×L(λ)dλ  (14)

In all color charts on the subject, if

Rs=Rc  (15)

Gs=Gc  (16)

Bs=Bc  (17)

are true, no error is included. If they are not true, a colorreproducibility error occurs. To remove this error, the following 3×3matrix coefficients $\begin{matrix}{\begin{pmatrix}{Rs} \\{Gs} \\{Bs}\end{pmatrix} = {\begin{pmatrix}{a11a12a13} \\{a21a22a23} \\{a31a32a33}\end{pmatrix}\quad \begin{pmatrix}{Rc} \\{Gc} \\{Bc}\end{pmatrix}}} & (18)\end{matrix}$

may be determined. These coefficients can be found by at least threetypes of typical color charts. The nine matrix coefficients of a11 toa33 are added to the image data provided by the image pickup machine 6.FIG. 47 shows data format examples of image files. The data format inExample 1 comprises the matrix coefficients added to the top of imagedata. The data format in Example 2 comprises the matrix coefficients andthe spectral sensitivity characteristic of the image pickup machine 6preceding the top of image data. The nine matrix coefficients of a11 toa33 are added to image file, whereby a color reproduction error can becompensated on a personal computer, etc., for example.

The data formats shown in FIG. 47 are examples and a similar effect isprovided if the matrix coefficients are added to any part of image data,needless to say.

The spectral sensitivity characteristic of the image pickup machine 6can be measured by the measurement method previously described in thesixteenth embodiment. Using the spectral sensitivity characteristiccorrected by the method described in the seventeenth or eighteenthembodiment, the precise matrix coefficients can be calculated and thecolor reproducibility error can be eliminated.

If the spectral distribution characteristic of a light source, L(λ), isa characteristic estimated from the light source type, correlated colortemperature, etc., there is no problem on practical use. In this case,however, the standard spectral distribution characteristic correspondingto the light source type needs to be obvious, and a spectraldistribution characteristic involving no problem on practical use isfound by correcting the standard spectral distribution characteristicaccording to the correlated color temperature. Resultantly, for thespectral distribution characteristic of a light source, L(λ), highlyaccurate color management can be easily realized with less information.

What is claimed is:
 1. A color characteristic measurement apparatus ofan image pickup machine, comprising a test chart as a subject to whichapplied light is applied from a front side; a black box being placed ona rear face of said test chart and formed on an inner surface in black;holes being made in said test chart and said black box; and a lightoutput section being placed in said black box at a position where saidlight output section can be observed through said holes from the frontof said test chart.
 2. The color characteristic measurement apparatus ofan image pickup machine as claimed in claim 1 further including meansfor changing a light quantity of light emitted from said light outputsection.
 3. The color characteristic measurement apparatus of an imagepickup machine as claimed in claim 1 further including spectrum meansfor making light from a light source a spectrum, wherein said lightoutput section emits the spectrum provided by said spectrum means. 4.The color characteristic measurement apparatus of an image pickupmachine as claimed in claim 3 wherein the light emitted from said lightoutput section is light changed in specific wavelength steps in aspecific wavelength range.
 5. The color characteristic measurementapparatus of an image pickup machine as claimed in claim 4 wherein thespecific wavelength step in which the light emitted from said lightoutput section is changed is roughly equal to a half-value width of thelight emitted from said light output section.
 6. The colorcharacteristic measurement apparatus of an image pickup machine asclaimed in claim 1 further including a filter having a specific spectraltransmittance characteristic, placed in front of said light outputsection.
 7. The color characteristic measurement apparatus of an imagepickup machine as claimed in claim 1 further including an external lightsource and an optical waveguide device for guiding light from saidexternal light source into said light output section in said black box.8. The color characteristic measurement apparatus of an image pickupmachine as claimed in claim 1 further including a diffuser panel beingplaced in front of said light output section for diffusing light.
 9. Thecolor characteristic measurement apparatus of an image pickup machine asclaimed in claim 1 further including an illumination light source beingplaced in front of said test chart for illuminating said test chart at aposition where said illumination light source does not apply light tosaid light output section through said hole in said test chart.
 10. Thecolor characteristic measurement apparatus as claimed in claim 1 furtherincluding: a second illumination light source being placed in front ofsaid test chart for applying light to said light output section throughsaid hole in said test chart, wherein output light from said lightoutput section and light which is applied from said second illuminationlight source and reflected on said light output section are emittedthrough said hole.
 11. The color characteristic measurement apparatus asclaimed in claim 6 further including: an illumination light source beingplaced in front of said test chart for applying light to said filterthrough said hole in said test chart, wherein output light from saidlight output section and light which is applied from said illuminationlight source and reflected on said filter are emitted through said hole.12. The color characteristic measurement apparatus as claimed in claim 6further including: an illumination light source being placed in front ofsaid test chart for applying light to said diffuser panel through saidhole in said test chart, wherein output light from said light outputsection and light which is applied from said illumination light sourceand reflected on said diffuser panel are emitted through said hole. 13.The color characteristic measurement apparatus as claimed in claim 1,wherein one color chart or a plurality of color charts different inreflectivity are placed on said test chart.
 14. The color characteristicmeasurement apparatus as claimed in claim 1, wherein one color chart ora plurality of color charts different in chromaticity are placed on saidtest chart.
 15. The color characteristic measurement apparatus asclaimed in claim 1, wherein a hole through which said light outputsection in said black box cannot be observed is made in said test chart.16. The color characteristic measurement apparatus as claimed in claim1, wherein a reference white color chart is placed in the proximity ofsaid hole in said test chart.
 17. A color characteristic measurementmethod of an image pickup machine, comprising the steps of: placing acolor characteristic measurement apparatus as claimed in claim 1 and afirst illumination light source so that light applied from the firstillumination light source is not applied to a light output section in ablack box; imaging a test chart of the color characteristic measurementapparatus by the image pickup machine; and finding a colorcharacteristic of the image pickup machine based on first datacorresponding to the area of the light output section, extracted frompicked up image data or second data provided by performing operation onthe first data.
 18. A color characteristic measurement method of animage pickup machine, comprising the steps of: placing a colorcharacteristic measurement apparatus as claimed in claim 13 and a firstillumination light source so that light applied from the firstillumination light source is not applied to a light output section in ablack box; imaging a test chart of the color characteristic measurementapparatus by the image pickup machine; and correcting first datacorresponding to the area of the light output section, extracted frompicked up image data or second data provided by performing operation onthe first data based on image data corresponding to the portion of onecolor chart or portions of a plurality of color charts different inreflectivity placed on the test chart.
 19. A color characteristicmeasurement method of an image pickup machine, comprising the steps of:placing a color characteristic measurement apparatus as claimed in claim14 and a first illumination light source so that light applied from thefirst illumination light source is not applied to a light output sectionin a black box; imaging a test chart of the color characteristicmeasurement apparatus by the image pickup machine; and correcting firstdata corresponding to the area of the light output section, extractedfrom picked up image data or second data provided by performingoperation on the first data based on image data corresponding to theportion of one color chart or portions of a plurality of color chartsdifferent in chromaticity placed on the test chart.
 20. A colorcharacteristic measurement method of an image pickup machine, comprisingthe steps of: placing a color characteristic measurement apparatus asclaimed in claim 2 and a first illumination light source so that lightapplied from the first illumination light source is not applied to alight output section in a black box; changing the light quantity oflight emitted through a hole in a test chart of the color characteristicmeasurement apparatus; imaging the test chart by the image pickupmachine, and finding a gradation characteristic of the image pickupmachine based on first data corresponding to the area of the lightoutput section, extracted from picked up image data or second dataprovided by performing operation on the first data.
 21. A colorcharacteristic measurement method of an image pickup machine, comprisingthe steps of: placing a color characteristic measurement apparatus asclaimed in claim 1 and a first illumination light source so that lightapplied from the first illumination light source is not applied to alight output section in a black box; changing the wavelength of aspectrum emitted through a hole in a test chart of the colorcharacteristic measurement apparatus; imaging the test chart by theimage pickup machine, and finding a spectral sensitivity characteristicof the image pickup machine based on first data corresponding to thearea of the light output section, extracted from picked up image data orsecond data provided by performing operation on the first data.
 22. Thecolor characteristic measurement method as claimed in claim 21, whereina characteristic relative to the wavelength of the light quantity of theemitted spectrum is found and the spectral sensitivity characteristic ofthe image pickup machine is corrected based on the found characteristic.23. The color characteristic measurement method as claimed in claim 21,wherein the light quantity of light emitted through the hole in the testchart of the color characteristic measurement apparatus is changed, thetest chart is imaged by the image pickup machine, a gradationcharacteristic of the image pickup machine is found based on first datacorresponding to the area of the light output section, extracted frompicked up image data or second data provided by performing operation onthe first data, and a spectral sensitivity characteristic of the imagepickup machine is corrected based on the found characteristic.
 24. In acolor characteristic measurement apparatus as claimed in claim 13wherein N color charts different in reflectivity (N is an integer of 2or more) are placed on a test chart, to change the light quantity ofemitted light, pick up images in sequence by an image pickup machine,and find a gradation characteristic of the image pickup machine, a colorcharacteristic measurement method comprising the steps of: adopting afirst image picked up when the emitted light is of a specific lightquantity as a reference image; adopting a part corresponding to an areaof a light output section in a second image picked up when the emittedlight is of any other light quantity as first data; finding a firstcolor chart of the N color charts with data in the second image greaterthan and closest to the first data; finding a second color chart of theN color charts with data in the second image smaller than and closest tothe first data; correcting the first data based on data of the partscorresponding to the first and second color charts in the first andsecond images to find second data; and finding the gradationcharacteristic of the image pickup machine from the second data at eachimage picking up time.
 25. In a color characteristic measurementapparatus as claimed in claim 13 wherein N color charts different inreflectivity (N is an integer of 2 or more) are placed on a test chart,to insert the color charts into a hole in the test chart one at a timein order, pick up an image for each color chart by an image pickupmachine, and find a gradation characteristic of the image pickupmachine, a color characteristic measurement method comprising the stepsof: adopting a first image picked up when a specific color chart isinserted into the hole as a reference image; in a second image picked upwhen any other color chart is inserted into the hole, adopting a partcorresponding to an area of the inserted color chart as first data;finding a first color chart of the N color charts with data in thesecond image greater than and closest to the first data; finding asecond color chart of the N color charts with data in the second imagesmaller than and closest to the first data; correcting the first databased on data of the parts corresponding to the first and second colorcharts in the first and second images to find second data; and findingthe gradation characteristic of the image pickup machine from the seconddata at each image picking up time.
 26. In a color characteristicmeasurement apparatus as claimed in claim 13 wherein N color chartsdifferent in reflectivity (N is an integer of 2 or more) are placed on atest chart, to change light emitted from a light output section inspecific wavelength steps in a specific wavelength range, pick up imagesin order by an image pickup machine, and find a spectral characteristicof the image pickup machine, a color characteristic measurement methodcomprising the steps of: adopting a first image picked up when theemitted light is of a specific wavelength as a reference image; adoptinga part corresponding to an area of an inserted color chart in a secondimage picked up when the emitted light is of any other wavelength asfirst data, finding a first color chart of the N color charts with datain the second image greater than and closest to the first data; findinga second color chart of the N color charts with data in the second imagesmaller than and closest to the first data; correcting the first databased on data of the parts corresponding to the first and second colorcharts in the first and second images to find second data; and findingthe spectral characteristic of the image pickup machine from the seconddata at each image picking up time.
 27. The color characteristicmeasurement method as claimed in claim 26 wherein an inverse function ofa gradation characteristic of the image pickup machine is found and alinear spectral characteristic of the image pickup machine is foundthrough the inverse function.
 28. Data transmitting apparatus fortransmitting a spectral sensitivity characteristic or correction datatherefor, the spectral sensitivity characteristic being obtained by thecolor characteristic measurement apparatus of claim
 1. 29. Datarecording apparatus for recording a spectral sensitivity characteristicor correction data therefor, the spectral sensitivity characteristicbeing obtained by the color characteristic measurement apparatus ofclaim
 1. 30. Data reproducing apparatus for reproducing a spectralsensitivity characteristic or correction data therefor, the spectralsensitivity characteristic being obtained by the color characteristicmeasurement apparatus of claim
 1. 31. Data transmitting apparatus fortransmitting a spectral sensitivity characteristic or correction datatherefor, the spectral sensitivity characteristic being obtained by thecolor characteristic measurement method of claim
 17. 32. Data recordingapparatus for recording a spectral sensitivity characteristic orcorrection data therefor, the spectral sensitivity characteristic beingobtained by the color characteristic measurement method of claim
 17. 33.Data reproducing apparatus for reproducing a spectral sensitivitycharacteristic or correction data therefor, the spectral sensitivitycharacteristic being obtained by the color characteristic measurementmethod of claim 17.